1. Field of Invention
The present invention relates to a data line driving circuit of an electro-optical panel, a control method thereof, an electro-optical device using these, and an electronic apparatus.
2. Description of Related Art
A conventional electro-optical device, for example, an active-matrix-type liquid-crystal display device, mainly includes a device substrate, on which a switching device is provided via pixel electrodes arrayed in a matrix, an opposing substrate, on which color filters, etc., are provided, and a liquid crystal which is provided between these two substrates. In such a structure, when a scanning line signal is applied to the switching device via scanning lines, the switching device is placed in a conducting state. During this conducting state, when an image signal is applied to the pixel electrode via data lines, a predetermined charge is stored in the liquid-crystal layer between the pixel electrode and the opposing electrode (common electrode). After the charge is stored, even if the switching device is turned off, the storage of the charge is maintained by the capacitance of the liquid-crystal layer if the resistance of the liquid-crystal layer is sufficiently high. In this manner, when each switching device is driven to control the amount of charge to be stored, the orientation state of the liquid crystal changes for each pixel, making it possible to display predetermined information.
In this case, since it may only be for a part of a period that the charge is stored in the liquid-crystal layer of each pixel, first, by having a scanning line driving circuit sequentially select each scanning line, and second, by supplying an image signal, obtained by converting image data into a line sequence and by a data line driving circuit performing DA conversion thereon to each data line time-division multiplex driving may be performed in which scanning lines and data lines are made common for a plurality of pixels becomes possible.
Here, the data line driving circuit includes a clock signal supply line, a shift register, an image data supply line, a sampling circuit, a first latch, a second latch, and a DA conversion circuit. The shift register sequentially shifts a transfer start pulse of a horizontal scanning period in accordance with a clock signal supplied via the clock signal supply line in order to generate each sampling signal corresponding to each data line. The sampling circuit samples image data supplied via the image data supply line in accordance with each sampling signal and supplies it to the first latch. The first latch maintains the sampled image data and creates point sequence image data. The second latch latches the point sequence image data in order to create the line sequence image data in accordance with a latch pulse of a horizontal scanning period and supplies this data to each data line.
In the above-described liquid-crystal display device, even if the switching device is turned off, the storage of the charge is maintained by the capacitance of the liquid-crystal layer. Concerning a particular pixel, if the gray scale value to be displayed in the pixel concerned is the same as that one field before, there is no need to supply an image signal to the pixel in the current field in order to newly re-store charge in the liquid-crystal layer. For this reason, by supplying an image signal to only a pixel in which there is a change between fields in order to rewrite the stored charge, reduction of the processing speed is possible, leading to reduced power consumption.
In such a liquid-crystal display device, it is necessary to specify a pixel in which there is a change between fields and to supply an image signal to a corresponding data line in a period in which the pixel concerned is selected by a scanning line signal. In this case, it is necessary to, by using an address decoder, specify the image data concerned by using a row address and a column address and to generate a scanning line signal and a data line signal from these addresses.
However, a problem arises that the circuit scale of the address decoder becomes large, and as a consequence, the power consumption is increased. In particular, a problem arises that even if an attempt to form an address decoder on a device substrate is made by using thin-film transistors (hereinafter referred to as xe2x80x9cTFTsxe2x80x9d), the circuit scale thereof is too large to be realized.
The present invention has been achieved in view of the above-described circumstances. An object of the present invention is to provide a data line driving method and apparatus suitable for reducing power consumption with a simple structure, an electro-optical device using the data line driving device, and an electronic apparatus in which this electro-optical device is used as a display.
To achieve the above-mentioned object, the data line driving circuit of the present invention is used for an electro-optical panel, which has a plurality of scanning lines, a plurality of data lines, and switching devices, and pixel electrodes arranged in such a manner as to correspond to the intersection of the scanning lines and the data lines and which is divided into blocks in units of a predetermined number of data lines. The data line driving circuit includes: a shift register section having a clock signal supply line that supplies a clock signal, a plurality of shift registers that sequentially shift a transfer start pulse in accordance with the clock signal in order to generate each sampling signal, the plurality of shift registers being provided in such a manner as to correspond to each of the blocks, and a selection circuit that selectively supply the transfer start pulse to each of the shift registers; an image data conversion section that samples image data in accordance with each of the sampling signals and converts the data obtained by performing sampling into line sequence image data after the data is latched; and a DA conversion section that outputs each data line signal obtained by performing DA conversion on the line sequence image data to each of the data lines.
According to the present invention, since the shift register section is divided into blocks by a plurality of shift registers, it is possible to selectively cause a necessary shift register to operate. Consequently, it is possible to reduce power consumption.
In the present invention, the sampling section may perform sampling in accordance with each of the sampling signals only when an enable signal supplied from the outside becomes active. In this case, since sampling is performed in accordance with an enable signal, for example, even if shift registers operate to generate sampling signals for a particular block, it is possible to sample image data only for a necessary dot from these signals.
Furthermore, in a case where the above-described data line driving circuit is controlled, preferably, image data is compared between horizontal lines which are adjacent in a data time-series manner, and supply of the clock signal is stopped for the block in which the data values match. Since the sampled image data is latched by the image data conversion section, when the image data values match between horizontal lines which are adjacent in a data time-series manner, it is not necessary to sample the image data again and to latch it. On the other hand, in order to perform sampling, it is necessary to cause the shift register to operate in order to generate a sampling signal by supplying a clock signal thereto, and parasitic capacitance occurs in the wiring which supplies the clock signal. Since the wiring acts as a capacitive load, in order to supply the clock signal at a sufficient through rate, a large amount of electric power is required. According to the present invention, since supply of the clock signal is stopped for the block in which the data values match, the power consumption can be greatly reduced.
In addition, in a case where the above-described data line driving circuit is controlled, preferably, image data is compared between horizontal lines which are adjacent in a data time-series manner, and supply of the image data is stopped for the block in which the data values match. Since the sampled image data is latched by the image data conversion section, when the image data values match between the horizontal lines which are adjacent in a data time-series manner, it is not necessary to sample the image data again and to latch it. On the other hand, parasitic capacitance occurs in the wiring which supplies the image data. Since the wiring acts as a capacitive load, in order to supply the image data at a sufficient through rate, a large amount of electric power is required. According to the present invention, since supply of the image data is stopped for the block in which the data values match, the power consumption can be greatly reduced.
Next, the electro-optical device according to the present invention includes: an electro-optical panel which has a plurality of scanning lines, a plurality of data lines, and switching devices and pixel electrodes arranged in such a manner as to correspond to the intersection of the scanning lines and the data lines, and which is divided into blocks in units of a predetermined number of data lines; a data line driving circuit that generates each data line signal to be supplied to each of the data lines; a scanning line driving circuit that generates each scanning line signal to be supplied to each of the scanning lines; and a control circuit that controls the data line driving circuit on the basis of image data. The control circuit includes: a determination section that compares the image data between horizontal lines which are adjacent in a data time-series manner in order to determine whether or not the data values match between the horizontal lines for each of the blocks and generates a determination signal which indicates the determination result for each of the blocks; and a clock signal generation section that generates, in accordance with the determination signal, a clock signal which becomes active only for the block in which there is a change in the data values between the horizontal lines. The data line driving circuit includes: a shift register section having a plurality of shift registers which sequentially shift the transfer start pulse of a block period in accordance with the clock signal in order to generate each sampling signal, the plurality of shift registers being provided in such a manner as to correspond to each of the blocks, a clock signal supply line that supplies the clock signal to each of the shift registers, and a selection circuit that supplies the transfer start pulse to each of the shift registers in accordance with a selection signal indicating to which block the image data corresponds; an image data conversion section that samples image data in accordance with each of the sampling signals and converts the data obtained by performing sampling into line sequence image data; and a DA conversion section that outputs each data line signal obtained by performing DA conversion on the line sequence image data to each of the data lines.
According to the present invention, it is determined whether or not the image data values match between horizontal lines which are adjacent in a data time-series manner, and based on the determination result, the clock signal is set to be active only for the block in which there is a change in the data values between the horizontal lines. Consequently, it is possible to reduce the electric power required to drive the clock signal supply line, making it possible to reduce the power consumption of the electro-optical device.
Furthermore, in the present invention, preferably, the determination section includes: a first line memory that stores image data; a second line memory that stores the image data which is previous by one horizontal scanning period; a comparison circuit that compares first image data read from the first line memory with second image data read from the second line memory in order to determine whether or not the data values match between horizontal lines for each of the blocks; and a determination memory that stores the determination result of the comparison circuit for each block, wherein the determination signal is generated by sequentially reading the determination result from the determination memory. In this case, it is possible to generate a determination signal with a simple structure.
Also, in the invention of the above-described electro-optical device, preferably, the control circuit includes an image data creation section that creates image data which becomes active only for the block in which there is a change in the data value between horizontal lines in accordance with the determination signal and that supplies the image data which is created via an image data supply line to the sampling section. In this case, since the image data is transmitted through the image data supply line only for the block in which there is a change in the data values, it is possible to reduce the electric power required to drive the image data supply line.
Also, in the invention of the above-described electro-optical device, preferably, the image data creation section creates a time-division signal in which the selection signal is interposed before the image data divided for each block and supplies this signal to the sampling section via the image data supply line. The shift register section includes a separation circuit that separates the selection signal from the time-division signal, and the sampling section samples the portion of the image data within the time-division signal. In this case, since the selection signal and the image data can be transmitted by one wire by using the time-division signal, it is possible to simplify the structure.
In addition, preferably, the time-division signal creation section causes the last logic level of the selection signal to continue for the block in which the image data becomes non-active. Since the time during which electric power is consumed in the logic circuit is the time when the logic level is changed, it is possible to reduce the power consumption by causing the logic level of the selection signal to continue.
Next, the electro-optical device according to the present invention includes an electro-optical panel having a plurality of scanning lines, a plurality of data lines, and switching devices and pixel electrodes arranged in such a manner as to correspond to the intersection of the scanning lines and the data lines; a data line driving circuit that generates each data line signal to be supplied to each of the data lines; a scanning line driving circuit that generates each scanning line signal to be supplied to each of the scanning lines; and a control circuit that controls the data line driving circuit in accordance with image data. The control circuit includes: a determination section that compares the image data between horizontal lines which are adjacent in a data time-series manner in order to determine whether or not the data values match between the horizontal lines for each dot; an enable signal generation section that generates, based on the determination result of the determination section, an enable signal which becomes non-active for a predetermined dot in which the data values match between the horizontal lines; and an image data creation section that outputs the image data to an image data supply line when the enable signal becomes active. The data line driving circuit includes: sampling sections each for sampling the image data in accordance with each sampling signal only when the enable signal becomes active; an image data conversion section that converts the data obtained by performing sampling by the sampling section into line sequence image data; and a DA conversion section that outputs each data line signal obtained by performing DA conversion on the line sequence image data to each of the data lines.
According to the present invention, since it is determined whether or not the data values change between horizontal lines which are adjacent in a data time-series manner in dot units and the image data is supplied to the image data supply line, it is possible to reduce the electric power required to drive the image data supply line even more.
Also, in the above-described invention, preferably, the determination section includes: a first line memory that stores image data; a second line memory that stores image data which is previous by one horizontal scanning period; a comparison circuit that compares first image data read from the first line memory with second image data read from the second line memory for each dot; and a determination memory that stores the determination result of the comparison circuit for each block.
Also, in the above-described invention, preferably, the enable signal generation section causes, based on the determination result of the determination section, the enable signal to become non-active when a predetermined number of dots in which the data values match between horizontal lines continue. According to the present invention, unless a certain amount of mismatching of the data values continues, the logic level of the enable signal does not change, and consequently, the power consumption required to drive the enable signal can be reduced. In a case where a match and a mismatch of the data values repeat in dot units, since matches have not occurred continuously, the enable signal does not become non-active, and no electric power is consumed to drive the enable signal, whereas when the number of dots in which a match occurs exceeds a predetermined number, the enable signal becomes non-active, making it possible to reduce the electric power required to drive the image data.
Furthermore, preferably, the image data creation section sets the level of the image data supply line to be constant when the enable signal becomes non-active.
In addition, preferably, the electro-optical panel is divided into each of blocks in units of a predetermined number of data lines. The control circuit includes a clock signal generation section that generates, based on the determination result of the determination section, a clock signal which becomes active only for a block in which there is a change in the data values between horizontal lines. The data line driving circuit includes a shift register section having a plurality of shift registers which each sequentially shift a transfer start pulse of a block period in accordance with the clock signal in order to generate each sampling signal and which correspond to each of the blocks, respectively, a clock signal supply line that supplies the clock signal to each of the shift registers, and a selection circuit that supplies the transfer start pulse to each of the shift registers in accordance with a selection signal indicating to which block the transfer start pulse corresponds.
Next, an electronic apparatus of the present invention uses the electro-optical device as a display section, and, for example, an applicable device is a view-finder used for a video camera, a portable phone, a notebook computer, and a video projector.